Multistage amplifier or receiver arrangement



June 6, 1933. E. GERLACH ,9

MULTISTAGE AMPLIFIER 0R RECEIVER ARRANGEMENT" Filed Nov. 5, 1927 INVENTOR ERWIN GERLACH ATTORNEY l as otherwise the frequency of the supply line r1 9 Patented June 6, 1933 1 UNITED STATES ERWIN GERLAGE, 0F EE LIN-sIEMENssrAn'r, GERMANY, AssIGNoR T0 sIEMENs a .HALSKE,AKTIENGESELLSCHAFT, or SIEMENSSTADT N AR BERLIN, GERMANY, A

ooRroRArIoN or GERMANY MULTIsrA E AMPLIFIER OR REGEIVER ARRANGEMENT Application filed November 5, 1927, Serial No. 231,224, and in Germany November 26 1926.

The object of the present invention is an amplifier or receiver circuit, arrangement comprising a plurality of tubes, which is particularly suited for being supplied from a power supply line. It is known that, according to formerpracticeflt has been necessary in schemes of the said'kind to heat thefirst tubes at least from separate batteries would manifest ,itself in an inconvenient and disturbing manner in the output circuit of the amplifier. Hence, feeding from a network was at most practicable or admissible for the endlstage only 7 e i Now, the essential feature of the invention consists in that the filaments of the first few tubes are heated by the plate current of the last; or power tube or the last few tubes. In, an arrangement of 1 this nature, the fila- Inent current of the first tubes will not vary any more at the rhythm or frequency of the network or. supply current, but only at that .of the audio or tonal frequenciesto be. transmitted, and these frequencies are so high in valuethatthey no longer produce a disturb ing action owing to thethermal inertia of the filaments. u i

For reasons ofpurity of transmission and avoidance of back-couplings, is lagood plan in circuitarrangements comprising a comparatively great number of stages to eliminate from the heating'or filament current of the first :tube also the audio-frequency component wholly or partly, A means to this end, for instance, would consist to provide conveniently in series with the filaments o fthe ifirst tube a sulficiently large condensfer to pass through it; the a. c. component of the plate current of the end tube or tubes varying duringthe operation of the amplifier and to thereby preclude the same from [the filaments To promote this action, ac-

cording to I the invention, choke-coils may further be; provided inserieswith the filaments. Another scheme would be to replace the said condenser suitably by a buffer battery, v M l A still more eifective means, according to the present invention, consists in forming thelaststageor stages of the tube amplifier ing choke-coils or condenser or bufl'erbatby tubes connected push-pull-fashion or in phase opposition whereby the total plate current flowing through the last stage or stages is made almost independent of the speech or voice currents, seeing that, at. a'given instant, any increase in the plate currentoit' one tube would correspond toa similar decrease in the of the potential V total plate current ofthe last pair of, tubes owingto small dilferences in these two tubes, the above-mentioned arrangement compristeries may be, used also'in this case. 1 One e advantageous way of practicing this scheme consists in connectingthe plate leads byway of corresponding choke-coils with both ends of the filament or the parallel connected filaments of the last tubes, if' desired, with the addition of a condenser, with the middle of the secondary winding of the heating-current transformer. l

Variations in the total plate current of the last pair of tubes also in the push-pull arrangement, can be eliminated to a certain extent by that a variable resistance is con nected, say, in parallel to the grid leak ,ortlie discharge path, for the purpose of compensating or neutralizing such differences as may be present in internal resistance, slope, etc. Another feature of the invention is thatthe potential fall in the heating circuits of'the first or input tubes is used forthepurpose of providing grid potential for allor some of the amplifier tubes. c In the drawing: 1 l l v Fig. 1 shows one embodiment of theinvention using a single power tube and Fig. 2 shows a push-pull arrangement whereby improved action is obtained.

One embodiment of the basic ideas of the invention is shown by way of example in the accompanying drawing Fig. 2 representing a push-pull arrangement for the end tubes. The amplifier is fed from an alternating current supply-line W. The current rectified in a rectifier g, after having passed through a rejector circuit (noise-killer) s inserted in known manner is fed to the plates of the different tubes. One part of the plate currents is conducted through a leak and the two halves of the primary winding of a repeater (transformer) u to the two end tubes 74 and 1 5 connected push-pull-fashion, whence it is conducted by way of choke-coils hand 7" and the series-connected filaments of the first tubes 11, 1"2,r3 (r1 being, for instance, an audion tube) to ground or the negative pole of the rectifier g. A sufficiently large condenser 0 is connected in parallel to all of the filaments, another choke-coil 6 between the filaments of tubes T3 and one of the junction points of the condenser c. The last push-pull arranged tubes may be heated by a. c. through a transformer it without any harmful consequences, the two filaments of said tubes being conveniently connected in parallel with the secondary winding of said transformer.

To regulate the grid potentials of the different tubes, the connection of the combined plate and filament leads I to ground contains a resistance 1). Furthermore, the grids of the different tubes are not directly connected by way of the secondary windings of the. transformers with the corresponding filaments, but with ground. In this manner, the potential fall across resistance o'acts as a biasing potential for the difl'erent grid circuits. The

said resistance 1) is suitably so proportioned that fluctuations in the total plate current in the joint lead Z are nearly eliminated'by incidentally produced variations in the grid biaslng potentials. In parallel relation to one of the push-pull-connected tubes, say r5, there is a fine-stepped resistance 20, the obect of which is to compensate slight discrepancies in the tube constants liable to lead to alterations or fluctuations in the total. plate current of the two push-pull-connected tubes upon the flow of speech currents through the amplifier. However, in an arrangement of this kind, 1t may happen that the plate current of the end tubes fails to suffice for the heating of the preceding tubes. i

This inconvenience, according to the present nvention, is eliminated by that a suitably variable resistance is connected in parallel to the last amplifier stage, said resistance being so proportioned that a current is caused to flow therethrough which, together with the plate current, results in and furnishes the desired heating current for the preceding tubes. So far as the insertion of the said resistance is concerned, it is immaterial whether the last amplifier stage consists of a single or simple tube or of a combination of push-pullconnected tubes.

Another embodiment of the basic idea of the invention is illustrated in the accompanying drawing Fig. 1. In this scheme, the last stage of the amplifier, r4, does not cons st of a push-pull connection, but rather of a slngle tube, a variable resistance a being arranged in parallel to the plate discharge path, 1n order to insure an adequately large heating current for the preceding tubes r1,r3. The a. c. taken, for instance, from a network W is rectified by a rectifier g, is then smoothed by choke-coils s and is finally fed through the tube r4 and resistance a to the precedlng tubes rl-rS. The fluctuations in the plate'" current also in this case are precluded from the filaments to be heated by means of chokecoils b, 7, and h and a parallel-connected condenser 0, the latter being optionally replaced by a buffer battery. The last or end (power) 6 tube may be heated with a. c; by way of a transformen In case the last stage consists of two push-pull-connected tubes, one of the latter may in addition be provided with a parallel resistance, for the object of regulat- 6 ing its own resistance.

As to the rest, in both cases the circuit arrangement is built up in the usual way.

The currents entering at e and to be amplified h may be fed or transferred from one stage of. the amplifier arrangement to the next either by means of transformer coupling, as shown in the drawing, or else by capacityresistance coupling, until they reach a. The

circuit connection scheme hereinbefore de scribed is useful also in the case of d. c. supply from a network.

Having thus described my inventlon what I desire to protect by Letters Patent is as follows:

1. In an amplification system, a'plurality of interlinked electron tube circuits, each of said tubes having grid, cathode and anode ies electrodes, and at least one of said tubes having larger power capacity than the others of said tubes, a supply circuit for furnishing the anode potential to all of said tubes, and a filtering circuit, a series circuit comprising the cathode electrodes of the tubes of less power capacity than the last mentioned of said tubes and including the anode electrode of at least oneof said tubes of larger power capacity, said supply circuit and said filtering circuit, means including at least one.

choke coil for connecting said last named cathode electrodes and the cathode electrode of said power tube, and a capacity shunted across said cathode circuit.

2. In an amplification system, a plurality of interlinked space discharge device circuits,

each ofsaid devices comprising a grid electrode, an anode and a cathode, and at least one of said space discharge devices having larger powercapacity than the others thereof, a supply circuit forfurnishing the anode potential to all of said space discharge devices, and a filtering circuit, a series circuit comprising the cathodes of the space discharge devices of less power capacity than said last mentioned space discharge devices and including the anode electrode of at least one of said space discharge devices of larger power capacity, said supply circuit and said filtering circuit, means including at least one choke coil for connecting said last named cathodes and the cathode of said power tube,

a capacity shunted across said cathode circuit, and a variable resistance shunted across the anode and cathode of said power space discharge device.

ERWIN GERLACH. 

